The Lancers returned to home bases in the U.S. in January. They flew only 3% of all strike missions against ISIS, but had dropped 40% of the bombs and other munitions. B-1s could loiter over the battlefield for 10 hours, much longer than jet fighters, and also could fly supersonic, reaching targets across Iraq and Syria within minutes.

“The B-1s are rotated out, so they're not here right now, they've gone back to do some upgrades," Lieutenant General Charles Q. Brown Jr., commander at U.S. Air Forces Central Command, told reporters.

Each B-52 can carry up to 70,000 pounds of payload, officials say. The aircraft, sometimes nicknamed the "Big Ugly Fat Fella," first took to the skies in 1954 and regularly takes part in military exercises around the world.